This invention relates to a method and appatatus for vulcanizing an elastomer product such as a tire for a motor vehicle using gas and steam as a pressurizing medium and a heating medium.
FIG. 9 shows a conventional method for vulcanizing an elastomer product such as a tire for a motor vehicle using gas as a pressurizing medium which comprises the steps of placing a tire 2 in a mold 1, bringing a bladder 3 in contact with the inner surface of the tire 2 with application of pre-shaping pressure, closing the mold 1 to bring the tire 2 in contact with the mold inner surface, heating the tire 2 under pressure by supplying steam as a heating medium, the steam being blown in a substantially horizontal direction from nozzles 59 provided in a central unit of the vulcanizing machine and communicated with a supply passage 70 into an inner space 6 of the tire 2 or vulcanizing chamber, stopping the supply of steam either when the temperature of the tire rises to a specified temperature or after the lapse of a predetermined period of time, and supplying combustion gas or nitrogen gas as a pressurizing medium at a pressure equal to or higher than that of the steam, the gas being blown in a horizontal directions from the nozzles 59 or pressurizing medium nozzles provided at the same level as the steam nozzles 59 and communicated with the supply passage into the inner space 6 of the tire 2.
In the conventional method in which steam is blown in a substantially horizontal direction, an amount of steam condenses in a lower portion of the inner space 6 without being discharged and tends to prevent the lower side wall of the tire 2 from rising in temperature. Pressurizing gas has a temperature lower than that of steam. A portion to which pressurizing gas is blown, e.g., the lower bead portion, is liable to be undesirably cooled. Additionally, pressurizing gas has a specific gravity greater than that of steam when being introduced and is accordingly liable to stay in a lower portion of the inner space 6. Consequently, the temperature of the lower side wall and lower bead portion of the tire which are in contact with low temperature gas becomes low. On the other hand, steam is liable to stay in an upper portion of the inner space 6 and comes to a high temperature because of being adiabatically compressed by pressurizing gas supplied at high pressure. This results in an undesirable rise in the temperature of the upper side wall of the tire 2. In the inner space 6, consequently, there are a layer 61 of steam in the upper portion, a layer 62 of gas in the lower portion, and a layer 63 of steam condensate in the lowermost portion. Accordingly, as shown FIG. 4a, for example, the temperature at point A on the upper bead portion of the tire 2 rises as shown by solid line 16 after gas is supplied, the temperature at point B on the lower bead portion of the tire 2 lowers as shown by solid line 15 after gas is introduced. Consequently, a great temperature difference, e.g., 13.degree. C., occurs between points A and B.
Also, as shown in FIG. 4b, the temperature at point C on the upper side wall of the tire 2 rises as shown by solid line 16a after gas is supplied, the temperature at point D on the lower side wall of the tire 2 does not rise as shown by a solid line 15a after gas is supplied. Consequently, a great temperature difference, e.g., 12.degree. C., occurs between points C and D.
After such a great temperature difference occurs, the temperature difference does not entirely disappear until the vulcanizing operation is completed. Accordingly, it could be seen that the vulcanization degrees of the upper and lower side walls of the tire 2 become different from each other. Such difference is undesirable to the quality of product. Moreover, since the necessary vulcanizing time of a tire is determined based on vulcanization of a lower portion of the tire where the temperature rises most slowly, an undesirable long time is required. It would be apparent that such a long time is disadvantageous as regards productivity and energy saving.